1. Field of the Invention
The present invention relates to an image processing apparatus for processing RGB Bayer array image data, an image pickup apparatus, a storage medium for storing an image processing program, and an image processing method.
2. Description of the Related Art
A single image pickup device is mostly used for a digital camera. For a digital video camera, a two or three image pickup device may be used, or the single image pickup device may be used.
If the single image pickup device as described above is a color image pickup device, the single image pickup device includes a mosaic color filter on an image pickup surface. Typical color filter arrays include, for example, an RGB Bayer array.
In RGB Bayer array image data obtained from the image pickup device of the RGB Bayer array as described above, some image pickup systems may have different amounts of noise in respective RGB channels. Then, the noise in one channel is more conspicuous than the noise in other channels and thus is observed as color noise, which may not be preferable for image quality.
As a method for solving such a problem, it is conceivable to perform a process for increasing a noise reduction amount for the channel with a large amount of noise. However, if the method as described above is used, a waveform of the channel with the increased noise reduction amount becomes obtuse and different from waveforms of other channels, which is another problem.
Generally, in a noise reduction process in which the process is performed within one frame, as the noise reduction amount is increased, resolution impression and sharpness impression of an image are degraded. As a result, it is known that a false color occurs at an edge portion of the image.
In order to suppress the occurrence of the false color as described above, it is conceivable to increase not only the noise reduction amount for a particular channel, but also the noise reduction amounts for all the channels similarly. However, in this case, while a total noise reduction effect increases, the resolution impression and the sharpness impression of the image are significantly degraded due to a reason as described above.
Consequently, Japanese Patent Application Laid-Open Publication No. 2003-123063 has proposed a color noise reduction technique in which no false color occurs at an edge. In the technique described in the publication, a process is performed in which a color difference signal is used to detect a color edge, noise reduction is not applied to the color edge so that the false color may not occur, and the color noise is reduced at other portions.